Firefox 20.0.1 doesn't show me any YouTube video (I guess it's supposed to be in the box in the bottom left hand corner right?).
IE 10 displays just the top corner of the video.
Chrome Version 26.0.1410.64 m gives me the "player is too small" error
This is all on Win7.

Opera 12.15 on Windows XP works, assuming that the video I'm supposed to see is "I Am Dynamite: Ms. Jones". Clicking on the video itself does not take me to YouTube, in violation of my expectations, but you've put a link at the bottom.

Win8, Chrome 28 and IE10, neither worked right (mostly). Chrome either gave me "player too small" or opened the video in a new tab on Youtube, or, mostly, did nothing when I clicked. IE "worked" except that it didn't scale; only showing the top left.

Only option I'm sure of that won't need re-upping then is if it was upload to a Youtube account you can access, de-monetize it entirely and make sure it doesn't think there's third-party content. Third-party content detected in the video can often mean ads no matter what. But this is based on embedding a video last week at 245x245: here (Youtube player embedded on bottom-left).

Although depending, that may not be an option, I get that. Which sucks. But as far as I've ever known in practice, it's: owning your own player > Vimeo > Youtube > anything else, generally.

I should clarify minorly that regarding Youtube's recommended min. of 230x230 or 230x200, then Janis recommendation of 268x201, etc., I'm taking it for granted that who know what the most optimal size is, especially if this is a result of such recent changes, and said changes may still be getting tweaked whatwith everyone's comments on how inconsistent the players is working. Just fuck all that noise and de-monetize particular videos you need/want at small sizes and nullify the whole issue if you can. Or start uploading to not Youtube, I guess.